Articulated vehicle hinge joints must withstand the substantial forces generated by loading, traveling, power train operation and vehicle weight. Ideally, the hinge assemblies should not be excessively bulky or heavy, and should be readily adjustable and replaceable.
A first prior art system uses spherical bearings, as shown in U.S. Pat. No. 3,806,158 to Casey. Spherical bearings function in the manner of a ball-and-socket, and are capable of withstanding large radial and thrust loads because of their large bearing surface contact area. However, spherical bearings are vulnerable to wear because they employ sliding contact. Abrasive contaminants from a construction or mining environment can exacerbate wear.
Roller bearings have been employed in prior art articulated vehicles to avoid the wear problems associated with spherical bearings. However, roller bearings have several disadvantages as applied in the prior art, including weight, bulk, and complexity of maintenance and replacement. One prior art system employs two roller bearing assemblies. The first assembly is a large main bearing having dual races of tapered rollers for transmitting a large portion of the radial load between the frame portions, and for carrying all of the vertical thrust load. The second assembly includes a vertically floating bearing that transmits only radial loads. The second bearing must float to accommodate tolerances between the frame weldments to which the bearings are attached. Sufficiently accurate spacing between the weldments is achievable only by costly machining of the weldment surfaces. If two similar tapered-roller bearing assemblies were attached to a vehicle frame having normal welding tolerance errors, unacceptable thrust pre-loading of the bearings would result, substantially diminishing the bearings' capacity to carry working loads.
A further disadvantage of conventional roller bearing designs is that the fixed main bearing must carry the entire thrust lead, making it bulky and heavy. While the floating bearing may be more compact and lightweight, the bulk and weight of the fixed bearing makes it undesirable for certain applications such as underground mining vehicles requiring compact dimensions. In addition, the frame itself must be larger and heavier at the weldments to which the fixed bearing is attached to transmit the entire vertical lead.
Prior art vehicle hinges using roller bearings are also difficult to service and replace. For maximum system rigidity, a tapered-roller bearing assembly is generally adjusted for a pre-load, meaning that the cone races are biased together to compress the bearing rollers between the cones and the bearing cup. To accommodate minor wear, it may be necessary to adjust the bearing to restore the pre-load to its desired level. Existing roller bearing assemblies require the removal and disassembly of the bearing assembly to adjust the pre-load. This process violates the bearing seal, exposing the interior of the assembly to contaminants, which is particularly a problem when adjustments are required in the field. Furthermore, complete replacement of a prior art bearing assembly usually requires at least two reinstallations to arrive at the proper shim to achieve the desired pre-load in the new bearing. Service and installation in the field also requires heavy, specialized tools that are not ordinarily available, and which would be costly to include on the vehicle.
Because of the foregoing problems associated with existing articulated vehicle hinge assemblies, there is a need for an effective articulated vehicle hinge that overcomes such problems. This, therefore, is the primary objective of the present invention.